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Floodplain Management

Corte Madera CreekThe Floodplain Management Ordinance of the Mill Valley Municipal Code (Title 18) regulates development within the floodplain by requiring new structures to comply with the regulations of the flood zone; and also by requiring any existing structures to comply with the Code, if a substantial improvement is proposed. The ordinance, which has been part of the Municipal Code since 1979, is a requirement for the City’s participation in the federal flood insurance program through the Federal Emergency Management Agency (FEMA). Periodically, FEMA updates the Flood Insurance Rate Maps (FIRM). These maps identify the boundaries of the 100-year floodplain and divide the floodplain into various “zones” based on the estimated depth of flood waters. A 100-year flood is the statistical probability, based on the review of historic rainfall and flood data, that there is a one percent chance in any given year that a flood of this magnitude will occur. Property located within designated “Special Flood Hazard Areas" (SFHAs) or within the “Regulatory Floodway”, as shown on the Flood Insurance Rate Maps, are subject to additional development restrictions and regulations based on the City’s Floodplain Management Ordinance and are also required to have flood insurance. The City’s participation with FEMA in regulating development in the floodplain can affect the availability of and rates for flood insurance for individual property owners.

Map Updates

Letter of Map Change (LOMC).  If a property owner has evidence that their property has been inadvertently mapped in a Special Flood Hazard Area (SFHA), or flood hazard data needs to be revised due to man-made changes, a request to FEMA for a Letter of Map Change (LOMC) may be submitted. Click here to download a flyer with more information.

FEMA Studies to update Marin County and Bay Area FEMA flood maps.  The City of Mill Valley is impacted by two FEMA studies due to its topography of hillsides, creeks, and proximity to Richardson Bay.  These two studies are the Riverine Flood Study and the San Francisco Bay Area Coastal Study. 

Riverine Flood Study (2013) Also called the "Mill Valley and Ross Valley Flood Study" was conducted from 2012-2013 and studied flooding from stormfall due to topography, hillsides, and creek capacity. The City of Mill Valley hosted a Community Meeting with FEMA and the County of Marin regarding this study, and the resulting revision to the Flood Insurance Risk Maps, including the creation of a regulatory floodway.  The presentation made by FEMA can be found here.  Changes to the FEMA foodplain map were finalized in September 2013 based on this study, and became effective March 17, 2014. Project details on the Riverine Study can be found on FEMA's website.

Currently underway:  San Francisco Bay Area Coastal Study (2014).  Also called the "Bay Coastal Study". This study is focuses on flooding due to stormwell and tides from the the coastline to inland areas. Official draft maps are available for review and will also be available at a community meeting scheduled for Thursday June 19, 2014 (6:30-9pm) at the Community Center.  Notification to those properties that are identified as part of the floodplain and possible floodway are underway with the formal comment and appeal period between June 4 and September 2, 2014. 

Further information FEMA Websites: Bay Coastal Study; general flood insurance informationNational Flood Insurance Program; Flood Hazard Mapping Program

Residents can also view the Special Flood Hazard Areas and proposed base flood elevation by viewing our local map application page, MarinMap.  Zoom to your specific parcel by selecting orange "I Want To" box and search by address or parcel number.  Then select "show layer list" to highlight the different FEMA information, including base flood elevations and floodplain designations. 

Frequently Asked Questions

Will your property be affected by the FEMA Map Updates?

Please click here for a list of those properies in the floodplain and floodway--Please note that there are possible modifications that may also impact the base flood elevations of properties.  Base flood elevations can be identified through the MarinMap link above or by contacting the Department of Public Works.

What is a Regulatory Floodway?

A regulatory floodway means the channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation by more than one foot. Structures located within Regulatory Floodways have additional development restriction beyond those imposed by being located within a floodplain. Note: All properties within the regulatory floodway are also in a floodplain and must follow the requirements of both designations.

Other Important Details for Homeowners in Floodplain Areas: Elevation Certificates and Home Improvement Projects

Flood Insurance & Elevation Certificates

Homes and buildings in high-risk flood areas with mortgages from federally regulated or insured lenders are required to have flood insurance. If you are required to  carry flood insurance and need to find a provider, FEMA operates a agent locator service that can be accessed online or by calling 1-888-379-9531. 

As part of securing flood insurance, some property owners may be required to get an Elevation Certificate.  An Elevation Certificate verifies the elevation data of a structure on a given property relative to the ground level. The Elevation Certificate is used by insurance agents and companies in the rating of flood insurance policies. If you need to have an elevation certificate completed, you will need to contact a licensed land surveyor. 

Home Improvements in the Floodplain -- Substantial Improvement Form Required

A substantial improvement is defined in the Municipal Code as, “any repair, remodel, rehabilitation, addition, or improvement the cost of which equals of exceeds 50 percent of the “depreciated market” value of the existing structure either, before the improvement is started, or if the structure has been damaged and is being restored, before the damage occurred.” If a structure is located in the floodplain, proof of the depreciated market value “reflected in an appraisal prepared by an independent professional appraiser” as well as the value of the proposed improvements (verified by the Cost Evaluation worksheet), must be provided to the Planning and Building Department along with the initial submittal for a building permit.

The Substantial Improvement worksheet must be accompanied by a current appraisal for the structure (from within one year), the Cost Evaluation worksheet, an itemized breakdown of the valuation of the project. The Substantial Improvement worksheet must be signed by both the property owner and the appraiser certifying that the information provided is accurate. The Planning and Building Department will then review the forms to ensure they have been filled out correctly and determine if the project is a substantial improvement. Over the counter permit applications to the Building Department will not have to complete the worksheet, unless it is the second over the counter building permit that has been submitted within a two year time period. Projects on structures within the floodplain are cumulative within two years.

Substantial Improvement FAQ’s:

Why am I required to fill out this worksheet?

The property on which you are proposing to do work is located within a Federal Emergency Management Agency (FEMA) designated floodplain determined by the latest FEMA map, which went into affect on May 4, 2009. All properties located within a floodplain must follow Chapter 18: Floodplain Management, of the Mill Valley Municipal Code.

What is the definition of a substantial improvement?

Substantial improvement means any repair, remodel, rehabilitation, addition, or improvement, the cost of which equals or exceeds 50 percent of the "depreciated market" value of the existing structure either, before the improvement is started, or if the structure has been damaged and is being restored, before the damage occurred.

What is the definition of the depreciated market value of a structure?

Depreciated value means the value of the structure only and does not include the land or any other accessory buildings or site improvements. It is the replacement cost of the existing structure less any depreciation that results from age or condition. For the purposes of the City’s floodplain management regulations the “market value” of a structure shall mean the same as “depreciated market value”.

How do I determine the valuation of my project?

To establish the value of any proposed improvements, a contractor shall submit an itemized breakdown of estimated material/labor costs and the Cost Evaluation form (attached to this packet). The contractor shall use the attached Material Receipts/Estimates handout to help them determine the valuation of the proposed project. These submitted documents and the project valuation will then be reviewed and approved by the Building Official in comparison to market value rates within Marin County and the City of Mill Valley.

What if the scope of work increases after my building permit is pulled?

The valuation of the project is cumulative. Therefore, if during construction changes are made to the permit; those valuations must be added to the total valuation submitted for the project. If during construction the project increases to over 50% of the depreciated market value of the structure, it must conform to the City’s current floodplain management regulations. Project valuations are cumulative for two years, meaning that all open permits for a structure are totaled together. A permit must be finaled for two years before a new project can begin to avoid it having a cumulative effect on valuation.

Do I need to fill out this form for a permit that is done over the counter?

Substantial improvements are typically not triggered by over-the-counter types of permits, so the first over-the-counter permit submitted for a property will not require these documents. However, since the valuation is cumulative for two years, if you pull an additional over-the-counter permit within that time frame you will need to fill out the form and include the total valuation of all the permits pulled in that two year period of time.

What if my project is a Substantial Improvement?

If the proposed repair, remodel, rehabilitation, addition, or improvement, equals or exceeds 50 percent of the depreciated market value of the existing structure it is considered a substantial improvement and you will be required to conform to Chapter 18 of the Mill Valley Municipal Code. Depending on the zoning and floodplain designation you may be required to flood proof the structure (commercial zones) or elevate the finished floor of the structure above the base flood elevation. If the proposed project is a substantial improvement you should speak to the Planning Department for more information and requirements.

Where can I get more information?

Chapter 18.04 of the Mill Valley Municipal Code

Additionally, for information on the Floodplain, Regulatory Floodway, or the Map Updates for properties within the City of Mill Valley you can contact the Planning Department at (415) 388-4033.

Last updated: 2/9/2015 10:21:39 AM